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United States Patent |
5,119,320
|
Ito
,   et al.
|
June 2, 1992
|
Cross coil type indicator
Abstract
In a cross coil type indicator having a pair of cross coils arranged in
quadrature, a magnet rotor having a shaft and a pointer attached to the
shaft and rotatably positioned within the coils, the pointer is positioned
to indicated a variable by flowing pulse currents through the coils in
which the duty ratio is related to the variable value. Digital data
corresponding to the pointer angle is stored as sin .THETA. or cos .THETA.
data in a read only memory to enable simple calculation of pointer
position from the duty ratio of the current pulse. A stop pin is provided
to limit rotation of the pointer at the end of the scale; a circuit is
provided for determining when the pointer is adjacent to the pin or will
be driven against the stop pin, and the drive currents are modified in
response to such conditions to reduce repetitive striking of the pin by
the pointer and to minimize the force with which the pointer is driven
against the pin at the stop pin end of the scale.
Inventors:
|
Ito; Tadao (Shizuoka, JP);
Ashizawa; Shouzo (Shizuoka, JP);
Ohishi; Shigeru (Shizuoka, JP)
|
Assignee:
|
Yazaki Corporation (JP)
|
Appl. No.:
|
389880 |
Filed:
|
August 4, 1989 |
Foreign Application Priority Data
| Nov 09, 1988[JP] | 63-145358[U] |
| Feb 06, 1989[JP] | 1-12185[U] |
Current U.S. Class: |
702/92; 324/154R |
Intern'l Class: |
G01R 001/38 |
Field of Search: |
324/154 R
364/571.01
|
References Cited
U.S. Patent Documents
3946311 | Mar., 1976 | Baker et al. | 324/167.
|
4051434 | Sep., 1977 | Sweet | 324/166.
|
4230984 | Oct., 1980 | Taylor | 324/115.
|
4356445 | Oct., 1982 | Congdon | 324/82.
|
4553093 | Nov., 1985 | Chikasue | 324/154.
|
4890057 | Dec., 1989 | Kobayashi et al. | 324/166.
|
4924178 | May., 1990 | Miyajima | 324/154.
|
Foreign Patent Documents |
0255772 | Feb., 1988 | EP.
| |
3003151 | Oct., 1980 | DE.
| |
58-24214 | May., 1983 | JP.
| |
63-145969 | Jun., 1988 | JP.
| |
63-23960 | Aug., 1989 | JP.
| |
Primary Examiner: Lall; Parshotam S.
Assistant Examiner: Cosimano; Edward R.
Attorney, Agent or Firm: Wigman & Cohen
Claims
What is claimed is:
1. A cross coil type indicator having a pair of cross coils arranged in
quadrature, a magnet rotor having a pointer at its center and rotatively
provided within the coils by resultant magnetic field generated by the
cross coils and capable of indicating a detected variable by flowing pulse
current in the coils in accordance with the detected variable and a
stopper pin for restricting the movement of the pointer at a low
rotational angle, wherein the indicator further comprises:
detection means for detecting whether or not the rotational angle of the
pointer falls within a predetermined range of angle .theta..sub.1 where
the pointer has a possibility of contacting with the stopper pin and for
providing an output signal in accordance with the result of the detection;
and
current control circuit means having its input connected to the output of
said detection means and its output connected to output circuit means for
driving the cross coils by pulse currents having duty ratios calculated by
duty ratio calculation circuit means, whereby only when the actual
rotational angle of the pointer is within the predetermined range of angle
.theta..sub.1, the amplitudes of the pulse currents from the output
circuit means are reduced by an output signal from said current control
circuit means.
2. An indicator including a pair of cross coils which are arranged so as to
be mutually perpendicular and a magnet rotor rotatably provided within the
coils, the magnetic rotor being adapted to be rotated by resultant
magnetic fields generated by flowing pulse currents corresponding to a
detected variable into the respective coils, thereby indicating the
detected variable with an angular rotation of the magnetic rotor, said
indicator further comprising:
means for storage and output of sin .theta. and cos .theta. data values
corresponding to the actual rotational angle .theta. of the magnetic rotor
responsive to the detected variable value, in which the data corresponding
to cos .theta. is obtained from the sin .theta. data by accessing to each
data of sin (90.degree.+.theta.);
means for generating pulse currents having duty ratios responsive to the
respective sin .theta. or cos .theta. data output values from the storage
and output means; and
output circuit means for driving the cross coils by flowing each of the
pulse currents to each coil, further including a pointer mounted to the
magnet rotor and a stopper pin means for restricting the movement of the
pointer, in which the indicator further includes means for restraining
contact noise between the pointer and the stopper pin caused by vibration
of the pointer when the pointer is near the stopper pin.
3. The indicator as claimed in claim 2, wherein the restraining means
comprises:
means for detecting if the rotational angle of the pointer falls within a
predetermined range of angle .theta..sub.1 where the pointer can contact
the stopper pin; and
means for reducing the amplitudes of the pulse currents supplied to the
cross coils by controlling the output circuit means only when the
detecting means detects that the actual rotational angle of the pointer is
within the predetermined angle .theta., thereby reducing the rotational
torque of the pointer to reduce the force with which the pointer contacts
the stopper pin.
4. The indicator as claimed in claim 2, wherein the restraining means
comprises:
means for detecting if the rotational angle of the pointer falls within a
predetermined range of angle .theta..sub.1 where the pointer can contact
the stopper pin; and
means for compensating the duty ratios of the pulse currents of the pulse
current generating means only when the detecting means detects that actual
rotational angle of the pointer is within the predetermined range of angle
.theta..sub.1, thereby reducing the rotational torque of the pointer to
reduce the force with which the pointer contacts the stopper pin.
5. An indicator including a pair of cross coils arranged in quadrature, a
magnet rotor having a pointer provided at its center and rotatable within
the coils by resultant magnetic fields generated by the cross coils and
capable of indicating a detected variable by flowing pulse currents in the
coils in accordance with the variable, and a stopper pin for restricting
the movement of the pointer at a low rotational angle, said indicator
further comprising:
means for 1) detecting if the rotational angle of the pointer falls within
a predetermined range of angle .theta..sub.1 where the pointer can contact
the stopper pin and for 2) providing an output signal in accordance with
the detected result;
output circuit means for driving the cross coils by pulse currents having
preliminary calculated duty ratios;
a current control circuit having an input connected to the output of said
detection means and an output connected to said output circuit means; and
a microprocessor having a central processing unit, random access memory,
and read only memory, said microprocessor being connected between the
detection means and the output circuit means, wherein digital data values
corresponding to angles of sin .theta. and cos .theta. for calculating the
duty ratios have been preliminarily stored in the read only memory,
whereby only when the actual rotational angle of the pointer is within the
predetermined range of angle .theta. are the amplitudes of the pulse
currents from the output circuit means reduced by an output signal from
said current control circuit means.
6. An indicator including a pair of cross coils arranged so as to be
mutually perpendicular, a magnet rotor having a pointer at its center and
rotatable within the coils by resultant magnetic fields generated by the
cross coils and capable of indicating a detected variable by flowing pulse
currents in the coils in accordance with the detected variable, and a
stopper pin for restricting the movement of the pointer, said indicator
further comprising:
means for producing sin .theta. and cos .theta. data values corresponding
to the actual rotational angle .theta. of the pointer responsive to the
detected variable;
means for generating pulse currents each having a duty ratio corresponding
to the respective sin .theta. and cos .theta. data values;
means for 1) detecting if the rotational angle of the pointer falls within
a predetermined angular range .theta..sub.1 where the pointer can contact
the stopper pin and 2) for providing an output signal in accordance with
the result of the detected result;
compensation means for compensating the duty ratios of the pulse currents
by controlling the pulse current generating means only when the detecting
means detects that the actual rotational angle of the pointer is within a
predetermined range of angle .theta..sub.1 ; and
an output circuit having an input connected to the output of the pulse
current generating means and an output connected to the cross coils for
supplying the pulse currents to the cross coils,
whereby when the actual rotational angle of the pointer is within the
predetermined range of .theta., the pulse currents having the compensated
duty ratios are produced from the output circuit, while when the
rotational angle is above the angle .theta., the pulse currents having
duty ratios without compensation are produced from the output circuit,
which currents then flow into the cross coils.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cross coil type indicator in which a
magnet rotor is rotated by a resultant magnetic field generated by cross
coils arranged in quadrature with each other and a detected variable is
indicated by a pointer rotated together with the rotor.
2. Description of the Prior Art
As shown in FIG. 1, the pointer driving portion of the cross coil type
indicator is, in general, comprised of a pair of coils L.sub.1 and L.sub.2
arranged in quadrature with each other, a magnet rotor Mg rotatively
provided in a resultant magnetic field generated by the two coils L.sub.1
and L.sub.2, a pointer A provided at one end of the rotary shaft (not
shown) mounted on the magnet rotor Mg, a scale plate B for indicating the
detected variable in cooperation with the rotating position of the pointer
A, a zero point stopper pin P which restricts the rotation of the pointer
A, and a spiral spring C for biasing the pointer A and the magnet rotor Mg
toward the stopper pin P.
With this construction, when drive currents i.sub.1 and i.sub.2 are flowed
through the cross coils L.sub.1 and L.sub.2 in quadrature as shown in FIG.
2, respectively, magnetic fields generated in each of the coils can be
represented by the following equations;
##EQU1##
Here, .mu..sub.1 and .mu..sub.2 indicate each magnetic permeability of the
coils L.sub.1 and L.sub.2, respectively,
n.sub.1 and n.sub.2 indicate the number of windings of the coils,
respectively, and
S.sub.1 and S.sub.2 indicate each cross-sectional area of the coils,
respectively.
On the other hand, since the magnet rotor Mg is rotated in the resultant
magnetic direction of the magnetic fields .phi..sub.1 and .phi..sub.2, its
rotation angle .alpha. can be represented by the following equation;
##EQU2##
When the coils L.sub.1 and L.sub.2 having an equal structure respectively
is used, the equation (2) can be rewritten as follows;
##EQU3##
That is to say, the rotation angle .alpha. is defined by the drive currents
i.sub.1 and i.sub.2.
Supposing that the drive currents i.sub.1 and i.sub.2 are
##EQU4##
then, the rotation angle .theta. corresponding to the resultant magnetic
field can be represented as follows;
##EQU5##
Namely, the rotation angle .theta. becomes equal to the rotation angle of
the pointer, i.e., .alpha.=.theta.. As a result, the direction of the
resultant magnetic field generated by the cross coils L.sub.1 and L.sub.2
becomes equal to the angle .theta. as shown in FIG. 3 and the magnet rotor
Mg is rotated up to the rotation angle .theta. against the biasing force
of the spiral spring C, which corresponds to the detected variable.
Accordingly, by reading the position of the pointer A which rotates
together with the magnet rotor Mg with respect to the scale plate B, it
becomes possible to know the value of the detected variable. It is to be
noted that the amplitudes of the drive currents i.sub.1 and i.sub.2 in
this case are determined by taking into consideration of the biasing force
of the spiral spring C.
In order to drive the cross coils as set forth above, it is necessary to
provide a drive unit for driving the cross coils. In this case, it is
preferable for the drive unit to be able to apply pulse currents of sin
.theta. and cos .theta. having duty ratios corresponding to the detected
variable to the cross coils as the drive currents. Further, in order to
lower production cost of the indicator, it is requested for the drive unit
to have a simple structure. Furthermore, if there is provided such a drive
unit in an cross coil type indicator, several problems coused in a
conventional cross coil type indicator can be settled since it becomes
possible to make degital processing of various data.
Hereinafter, one of the problems will be described with reference to the
drawings.
FIGS. 4 to 6 show one of prior art indicators having a drive unit which can
apply pules currents having duty ratios corresponding to the detected
variable.
Namely, in the drive unit of the cross coil type indicator as shown in FIG.
4, pulse currents having duty ratios corresponding to the detected
variable are generated, and they are applied to the cross coils L.sub.1
and L.sub.2 through an output circuit 50.
The drive unit comprises a sensor 10 for detecting a variable such as car
speed, a frequency/voltage (F/V) converter 20, a duty ratio calculating
circuit 30, a duty pulse generating circuit 40 and an output circuit 50.
The cross coils L.sub.1 and L.sub.2 and the magnet rotor Mg are the same
as those indicated in FIG. 1.
In operation, an output signal such as vehicle speed from the sensor 10 is
applied to the frequency/voltage (F/V) converter 20, where the frequency
of the output signal is converted into a D.C. voltage. The D.C. voltage
thus converted is applied to a duty ratio calculating circuit 30, where
sin .theta. and cos .theta. of the rotation angle .theta. of the pointer A
are sought in accordance with the voltage. Then, each duty ratio shown in
FIG. 5 is calculated therein from duty characteristics which change in
accordance with sin .theta. and cos .theta.. Each of the duty pulses is
generated in the duty pulse generating circuit 40 and pulse currents
having duty ratios are applied to the coils L.sub.1 and L.sub.2 through
the output circuit 50, respectively.
Since the pulse currents i.sub.1 and i.sub.2 are proportional to sin
.theta. and cos .theta. and the angle .alpha. of the resultant magnetic
field is changed in accordance with the detected variable, the pointer A
is rotated against the biasing force of the spiral spring in the direction
of the resultant magnetic field vector, thus enabling the read-out of the
rotation angle of the pointer A from the scale plate B.
Now, as stated previously a stopper pin P is provided at a position near
the zero indicating position as shown in FIG. 1 and the pointer A is
normally biased by the spiral spring C toward the stopper pin P. As a
result, when the pointer A is situated near the zero indicating position
in the case of a speed meter or "E" position in the case of a fuel
indicator, the pointer A comes into contact with the stopper pin P. Since
a desirable linearity in indication cannot be maintained in the vicinity
of "zero" or "E" position on the scale plate B, the "zero" or "E" position
has to be shifted to a higher position which is normally about 5.degree.
to 10.degree. above from its actual position, and the stopper pin position
must also be shifted to the corresponding position. Because of this
situation, noise is generated by repeated abutments between the pointer
and stopper pin due to the reasons which will be explained later.
FIG. 6 indicates a detailed circuit construction of the output circuit 50
shown in FIG. 4. In the output circuit 50, two pairs of the NPN
transistors Q11, Q13 and Q12, Q14 are connected in the form of a first
bridge circuit together having the first coil L.sub.1, and another two
pairs of the NPN transistors Q21, Q23 and Q22, Q24 are connected in the
form of a second bridge circuit having the second coil L.sub.2 between the
power supply +Vcc and the ground. Each base of the transistors Q11 through
Q24 is connected to the duty pulse generating circuit 40.
In operation, when each of the pulse currents i.sub.1 and i.sub.2 is
desired to flow through the coils L.sub.1 and L.sub.2 in the direction of
the solid line shown in FIG. 6, the transistors Q11, Q14 are turned on and
the transistors Q21, Q24 are turned off, while the transistors Q21, Q24
are turned on and the transistors Q22, Q23 are turned off by the
application of pulse signals to the base of each transistor from the duty
pulse generating circuit 40.
On the other hand, when the pulse currents i.sub.1 and i.sub.2 as the drive
currents are desired to flow through the coils L.sub.1 and L.sub.2 in the
direction of the dotted line shown in FIG. 6, the transistors Q12, Q13 are
turned on and the transistors Q11, Q14 are turned off while the
transistors Q22, Q23 are turned on and the transistors Q21, Q24 are turned
off.
Since the pointer A is driven by the pulse currents flowing through the
coils L.sub.1 and L.sub.2, which are responsive to the changes in the duty
ratios or the detected variable, the pointer A is subject to a vibration
generated by the changes and therefore noise is generated when the pointer
A strikes the stopper pin P. Especially, when the indicator is applied to
a speed meter, under the low speed condition the pointer A is constructed
in such a manner that it never comes off from the stopper pin so that on
and off action is repeatedly happened between the pointer A and the
stopper pin P at a low speed condition due to the vibration in the changes
of the detected variable, and noise is generated thereby.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a
cross-coil type indicator having a drive unit for driving cross coils,
which has a simple structure so as to produce it with low cost.
It is a second object of the present invention to provide a cross-coil type
indicator in which the duty ratios of pulse currents are calculated by
digital data corresponding to rotational angles .theta. of the pointer of
the indicator, and its sin .theta. and cos .theta., which have been
preliminarily stored in a ROM and read from the ROM, and pulse currents
having each duty ratios responsive to a detected variable are generated in
a duty pulse generating circuit and they are applied to cross coils in
quadrature, thereby simplifying the duty ratio calculation.
It is a third object of the present invention to provide a cross coil type
indicator having a stopper pin for restricting the rotational movement of
a pointer of the indicator in which detection means for detecting whether
or not actual rotational angles of the pointer of the indicator fall
within a predetermined range of angles and for producing an output signal
in accordance with the result of the detection, and compensation means for
compensating the duty ratios of the pulse currents to be applied to the
cross coils are provided, whereby only when the actual rotational angle of
the pointer falls within the predetermined range of angle, the
compensation means compensates for the duty ratios of the pulse currents,
so as to reduce the torque of the pointer and to suppress the generation
of noise caused by repeated abutments between the pointer and the stopper
pin.
In order to achieve the first and second objects, a cross coil type
indicator having a drive unit includes a pair of cross coils arranged in
quadrature, and a magnet rotor having a pointer at its center and
rotatively provided within the coils by a resultant magnetic field
generated by the coils and capable of indicating a detected variable by
flowing pulse currents in the coils in accordance with the detected
variable, wherein the indicator further comprises: data generating means
for generating sin .theta. and cos .theta. data in accordance with the
actual rotational angle of the pointer responsive to the detected
variable, a ROM forming the data generating means; pulse generating means
for generating pulse currents having duty ratios corresponding to the sin
.theta. and cos .theta. thus generated and to be applied to the cross
coils; and output circuit means for driving the coils in accordance with
the pulse currents thus generated.
According to the cross coil type indicator with a drive unit having the
above structure, data processing is performed in the single ROM forming
the data generating means, it becomes possible to simplify its structure,
thus leading to a reduction in manufacturing cost. Further, according to
this cross coil type indicator, since only sin .theta. data within the
range of 0.degree..ltoreq..theta..ltoreq.90.degree. is to be stored in the
ROM, it becomes possible to have high resolutional indication
characteristic by a ROM having a certain capacity in comparison with the
cases in which the other data is stored therein.
Further, in order to achieve the third object, a cross coil type indicator
of the present invention includes a pair of cross coils arranged in
quadrature, a magnet rotor having a pointer at its center and rotatively
provided within the coils by a resultant magnetic field generated by the
cross coils and capable of indicating a detected variable by flowing pulse
currents in the coils in accordance with the detected variable and a
stopper pin for restricting the movement of the pointer at a low
rotational angle, wherein the indicator further comprises: detection means
for detecting whether or not actual rotational angles of the pointer of
the indicator fall within a predetermined range of angle, where the
pointer has a possibility of contacting with the stopper pin, and for
providing an output signal in accordance with the result of the detection;
and a current control circuit means having its input connected to the
output of the detection and its output thereof connected to an output
circuit means for driving the cross coils by pulse currents having duty
ratios calculated by a duty ratio calculation circuit means, whereby only
when the former angle of the pointer is within the predetermined latter
angle, the amplitudes of the pulse currents from the output circuit means
are reduced by an output signal from the current control circuit means.
According to the cross coil type indicator having the above structure, it
becomes possible to suppress generation of noise caused by repeated
abutments between the pointer and stpeer pin within the predetermined
range of the angle of the pointer.
These objects, features, and advantages of the invention will be better
understood from the following description with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a basic construction of the cross coil type indicator having
cross coils, a magnet rotor with a pointer, a bias spring and a scale
plate, according to a prior art;
FIG. 2 shows the cross coils through which drive currents flow;
FIG. 3 shows a resultant magnetic field of the magnetic fields generated by
the cross coils;
FIG. 4 shows a drive unit for the cross coils according to a prior art;
FIG. 5 shows the characteristics of duty ratios of sin .theta. and cos
.theta. about the currents to be applied to the cross coils;
FIG. 6 shows a detailed description of the output circuit shown in FIG. 4;
FIG. 7 shows one example of a drive unit for a cross coil type indicator
according to the present invention;
FIG. 8 shows the other embodiment of a drive unit for a cross coil type
indicator according to the present invention;
FIG. 9 shows the characteristics between pointer torque and rotational
angle of the pointer;
FIG. 10 shows another embodiment of a drive unit for a cross coil type
indicator according to the present invention;
FIG. 11 is a control flow chart of the microprocessor shown in FIG. 9;
FIG. 12 shows one embodiment of the output circuit and a current control
circuit according to the present invention;
FIG. 13 shows still another embodiment of a drive unit for a cross coil
type indicator according to the present invention;
FIG. 14 shows a further embodiment of a drive unit for a cross coil type
indicator according to the present invention;
FIG. 15 shows the duty ratios of the currents without compensation;
FIG. 16 shows the compensated duty ratios of the currents to be applied to
the cross coils; and
FIG. 17 is another control flow chart of the microprocessor shown in FIG.
14.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the accompanying drawings, preferred embodiments of the
present invention will be described.
FIG. 7 shows an embodiment of a drive units for driving cross coils L.sub.1
and L.sub.2 by pulse currents of sin .theta. and cos .theta. generated by
a sin .theta. function generator of a ROM.
The drive unit comprises a clock circuit 1, a counter circuit 2, a sin
.theta. function generator circuit 3, a sin .theta. duty pulse generator
4, a cos .theta. duty pulse generator 5, a first drive circuit 6, a second
drive circuit 7, and a direction setting circuit 8. The cross coils
L.sub.1 and L.sub.2 arranged in quadrature with each other are constructed
in the same manner as those indicated in FIG. 1.
In operation, a rectangular signal, the time period of which varies in
accordance with the detected variable such as vehicle speed and clock
signals are applied to the counter circuit 2. The output signal from the
counter circuit 2 is applied to the sin .theta. function generator circuit
3 and the sin .theta. function signal from the function generator circuit
3 of a ROM is applied to sin .theta. duty pulse generator circuit 4
directly, so as to generate a sin .theta. duty pulse therefrom.
On the other hand, the sin .theta. function signal is indirectly applied to
the cos .theta. duty pulse generator 5. Namely, the sin .theta. function
signal from the function generator circuit 3 is applied to the drive
circuit 7 after shifting the phase of the sin .theta. output signal by
90.degree. by phase shift means (not shown) according to the principle of
sin (90.degree..+-..theta.)=cos .theta..
The pulse currents thus generated by the sin .theta. duty pulse generator 4
and cos .theta. duty pulse generator 5 are applied to the coils L.sub.1
and L.sub.2 through the drive circuits 6 and 7, respectively.
The direction setting circuit 8 determines the direction of the drive
currents flowing through the cross coils L.sub.1 and L.sub.2 in accordance
with the output signal from the counter 2 circuit. The following table 1
indicates the relationship among the quadrant, angles, and the connection
of the output terminals in the drive circuits 6, 7.
TABLE 1
______________________________________
DIGITAL QUADR- OUTPUT TERMINALS
DATA ANT ANGLE a.sub.1
a.sub.2
b.sub.1
b.sub.2
______________________________________
0-90 1 0.degree.-90.degree.
i.sub.1
G i.sub.2
G
90-180 2 90.degree.-180.degree.
i.sub.1
G G i.sub.2
180-270 3 180.degree.-270.degree.
G i.sub.1
G i.sub.2
270-360 4 270.degree.-360.degree.
G i.sub.1
i.sub.2
G
______________________________________
(Note) G indicates the ground level.
As shown in the table 1, the output terminals a.sub.1, a.sub.2, b.sub.1,
and b.sub.2 of the drive circuits 6 and 7 are selected in accordance with
the digital data from the counter circuit 2. Since each of the currents
i.sub.1 and i.sub.2 flowing through the coils correspond to sin .theta.
and cos .theta., the direction of the resultant magnetic field vector
varies according to the detected variable. Accordingly, the magnet rotor
Mg is rotated in the direction of the resultant magnetic field.
The sin .theta. function generator circuit 3 can be formed by a ROM. Each
of the digital data corresponding to angle .theta. of sin .theta. data has
preliminarily been stored in the ROM as shown in the following table 2.
TABLE 2
______________________________________
DIGITAL DATA ANGLE .THETA..degree.
sin .THETA.
(cos .THETA.)
______________________________________
0 180 180 360 0 0 1
. . . . . . .
. . . . . . .
. . . . . . .
30 150 210 230 30 0.5
0.85
. . . . . . .
. . . . . . .
. . . . . . .
90 90 270 270 90 1 0
______________________________________
Here, the angle .theta. corresponding to the digital data "0" is set to
0.degree., and rate of change of the degital data (in this table "1")
corresponds to angle 1.degree., of which sin .theta. data is in the ROM.
Further, the sin .theta. data has been stored within the range of
0.degree..ltoreq..theta..ltoreq.90.degree. in the table 2. The sin .theta.
data within the ranges of 90.degree..ltoreq..theta..ltoreq.180.degree.,
180.degree..ltoreq..theta..ltoreq.270.degree. and
270.degree..ltoreq..theta..ltoreq.360.degree. are corresponding to the sin
.theta. data within the range of
0.degree..ltoreq..theta..ltoreq.90.degree., respectively.
However, it is also possible to store the sin .theta. data between
0.degree..ltoreq..theta..ltoreq.360.degree., as shown in the following
table 3.
TABLE 3
______________________________________
DIGITAL DATA ANGLE .THETA..degree.
sin .THETA.
(cos .THETA.)
______________________________________
0 0 0 1
. . . .
. . . .
. . . .
30 30 0.5 0.85
. . . .
. . . .
. . . .
90 90 1 0
. . . .
. . . .
. . . .
150 150 0.5 -0.85
. . . .
. . . .
. . . .
180 180 0 -1
. . . .
. . . .
. . . .
210 210 -0.5 -0.85
. . . .
. . . .
. . . .
270 270 -1 0
. . . .
. . . .
. . . .
330 330 -0.5 0.85
. . . .
. . . .
. . . .
360 360 0 1
______________________________________
In the case of the table 3, since current flowing direction can be set by
adopting output terminals a.sub.1 to b.sub.2 of the drive circuits 6, 7
based on the sin .theta. (cos .theta.) data, the direction setting circuit
8 can be omitted. The cos .theta. data can be obtained from the sin
.theta. data by shifting the phase of the sin .theta., but the cos .theta.
data may also be stored in the ROM.
Each of the pulse currents having duty ratios responsive to the detected
variable can be generated from the sin .theta. duty pulse generator 4, and
the cos .theta. duty pulse generator 5 in accordance with the sin .theta.
data and the cos .theta. data read from the ROM.
FIG. 8 shows the other embodiment of the cross coils type indicator
according to the present invention. The indicator comprises a detection
circuit 60 for detecting the amplitude of D.C. voltage from a
frequency/voltage converter (F/V converter) 20 and a current control
circuit 70 responsive to an output signal from the detection circuit 60
for controlling the amplitude of the pulse currents produced from an
output circuit 50.
In FIG. 8, the same reference numerals indicate the same constructing
elements as shown in FIG. 4. Namely, reference numeral 10 indicates a
sensor for detecting a variable such as vehicle speed, engine speed and
for producing a pulse signal, the frequency of which is responsive to the
detected variable. Numeral 30 indicates a duty calculating circuit, 40 a
duty pulse generating circuit, L1 and L2 cross coils, and Mg a magnet
rotor.
In operation, a pulse signal is produced from the sensor 10 in accordance
with the detected variable and it is applied to the F/V converter 20. The
pulse signal is converted into a D.C. voltage by the F/V converter 20 and
the output therefrom is applied to the detection circuit 60 on one hand,
and to the duty calculating circuit 30 on the other hand. The detection
circuit 60 detects the condition that whether or not actual rotational
angles of the pointer responsive to the detected variable fall within a
predetermined range of angles, e.g., between 0.degree. and 10.degree.,
where the pointer A of the indicator has a possibility of contacting with
the stopper pin P when the drive currents are initially applied to the
cross coils L.sub.1 and L.sub.2, such as at a low range of angles of the
pointer.
When the output signal from the F/V converter 20 do not fall within the
predetermined range of angle, that is to say angle .theta..sub.1, pulse
currents having duty ratios calculated by the duty calculating circuit 30
are produced from the duty pulse generating circuit 40 and the output from
the detection circuit 60 causes the current control circuit 70 to operate.
As a result, the current produced from the output circuit 50 has to be
applied to the coils L1 and L2 to decrease.
FIG. 9 indicates the relationship between the pointer rotational angle
.theta. and the pointer torque. As shown in FIG. 9, when the rotational
angle .theta. of the pointer A falls within the range of the angle
.theta..sub.1 where the pointer A may contact with the stopper pin P, the
amplitude of the pulse currents to be applied to the coils L1 and L2 are
reduced. As a result, the torque of the pointer A is decreased so that the
mechanical force of the pointer A which tends to contact the pointer A
with the stopper pin P is also weakened, thus preventing the generation of
noises. Since the low indication area near zero indication has generally a
low accuracy, the decrease in the torque causes no problem.
FIG. 10 shows another embodiment of the cross coil type indicator according
to the present invention. In this embodiment, a microprocessor having a
CPU (central processing unit), a RAM, and a ROM is used instead of the F/V
converter 20, the duty calculation circuit 30 and the detection circuit 60
in FIG. 7. In this case, a pulse signal from the sensor 10 is directly
applied to the microprocessor 80.
FIG. 11 shows a program flow chart of a control to be performed in the CPU
of the microprocessor 80.
The operation of the CPU of the microprocessor 80 will now be made with
reference to the flow chart of FIG. 11.
In step S.sub.1, the frequency of the pulse signal from the sensor
.theta..sub.1 is calculated and the operation moves to step S.sub.2, where
the rotational angle .theta. is calculated in accordance with the
frequency. Then, the operation moves to step S.sub.3, where the duty
ratios of the pulse currents are calculated in accordance with sin .theta.
and cos .theta. of the rotational angle .theta. and the operation now
moves to step S.sub.4.
In step S.sub.4, a decision making is carried out about whether or not the
duty ratios thus calculated are within a predetermined angle range
.theta..sub.1. If the result of the decision is YES, that is, when the
duty ratios are above the angle range .theta., the operation moves to step
S.sub.5, where the duty pulses are generated from the duty pulse
generating circuit 30 to the output circuit 50.
On the other hand, if the result of the decision in step S.sub.4 is NO,
that is, when the duty ratios are within the angle range .theta..sub.1,
the operation moves to step S.sub.6, where the current control circuit 70
is energized by an output signal from the microprocessor 80 and the
amplitude of each pulse current to be produced from the output circuit 50
is reduced. As a result, the rotational torque of the pointer A is also
reduced. It is to be noted in this case that the biasing force of the
spiral spring C of the pointer A (see FIG. 1) has to be taken into
consideration, when calculating the duty ratios corresponding to the
rotational angle of the pointer A.
FIG. 12 indicates a detailed circuit of the output circuit 50 and the
current control circuit 70 shown in FIGS. 8 and 10, according to the
present invention. The construction of the control circuit 50 is same as
the one shown in FIG. 6. Therefore, a detailed explanation of the function
of the output circuit 50 will not be necessary.
In FIG. 12, the current control circuit 70 comprises a transistor Q.sub.1
and a resistor R.sub.1 connected in parallel between the power supply +Vcc
and the input of the output circuit 50. The base of the transistor Q.sub.1
is connected to the detection circuit 60 in FIG. 8 or to the
microprocessor 80 in FIG. 10, and the collector and emitter of transistor
Q.sub.1 are connected through the resistor R.sub.1.
In operation, when the rotational angle of the pointer A is above the
predetermined angle .theta..sub.1, the output signal from either the
detection circuit 60 or the microprocessor 80 is applied to the base of
the transistor Q.sub.1. Then, the transistor Q.sub.1 is rendered
conductive and the power supply +Vcc is directly connected to the output
circuit 50. Accordingly, the circuit construction in this case becomes
equivalent to the circuit construction shown in FIG. 6 and the pulse
currents having the duty ratios corresponding to the rotational angle of
the pointer A flow through the coils L.sub.1 and L.sub.2.
On the other hand, when the rotational angle of the pointer is within the
predetermined angle .theta..sub.1, the output signal from either the
detection circuit 60 or the microprocessor 80 is not applied to the base
of the transistor Q.sub.1. As a result, the transistor Q.sub.1 is not
rendered conductive, so that the resistor R.sub.1 is inserted between the
power supply +Vcc and the input of the output circuit 50. Consequently,
the amplitude of the pulse currents i.sub.1 and i.sub.2 to be applied to
the coils L.sub.1 and L.sub.2 are decreased, compared with the former case
where the resistor R.sub.1 is short-circuited or branched by the
transistor Q.sub.1, thus reducing the torque of the pointer A and
preventing the noise from being generated.
FIG. 13 shows another embodiment of the cross coil type indicator according
to the present invention. In this embodiment, when the rotational angle of
the pointer A falls within the predetermined range of the angle .theta.,
the duty ratios of the pulse currents to be applied to the coils L.sub.1
and L.sub.2 are reduced.
In FIG. 13, the cross coil type indicator comprises a detection circuit 60
and a current control circuit 70. The remaining construction elements such
as sensor 10, F/V converter 20, duty calculation circuit 30, duty pulse
generating circuit 40, output circuit 50 are the same as those shown in
FIG. 8 and the same reference numerals are used thereto.
The input of the detection circuit 60 is connected to the output of the F/V
converter 20, while the output of the detection circuit 60 is connected to
the input of the current control circuit 70, so as to compensate for the
duty ratios of pulse currents to be applied to the coils L.sub.1 and
L.sub.2 in accordance with the output signal from the detection circuit
60.
In operation, the detection circuit 60 detects the output signal from the
F/V converter 20, i.e., D.C. voltage responsive to a measured variable and
determines if the rotational angle of the pointer A is within the
predetermined range of angle .theta., where the pointer A has a
possibility of contacting with the stopper pin p (see FIG. 1).
When the rotational angle is above the predetermined range of angle
.theta..sub.1, no output signal from the detection circuit 60 is produced
and no compensation operation is performed to the duty ratios of the pulse
currents to be applied to the coils L.sub.1 and L.sub.2 through the
compensation circuit 70. Namely, the duty ratios calculated by the duty
calculation circuit 30 is directly applied to the duty pulse generating
circuit 40 without compensation and the pulse currents having the duty
ratios without compensation generated by the circuit 40 are applied to the
coils L.sub.1 and L.sub.2 through the output circuit 50.
On the other hand, when the rotational angle of the pointer A is within the
predetermined range of angle .theta..sub.1, an output signal is produced
from the detection circuit 60 and it is applied to the current control
circuit 70. The duly ratios calculated by the duty calculation circuit 30
are multiplied by a predetermined coefficient .beta.(0<.beta.<1) and
modified duty ratios thus multiplied are applied to the duty pulse
generating circuit 40. As a result, the pulse currents having the modified
duty ratios are generated from the circuit 40 and applied to the coils
L.sub.1 and L.sub.2 through the output circuit 50. This means that the
torque of the pointer A is decreased and the generation of the noise sound
is prevented since the force which tends to contact the pointer A with the
stopper pin p is weakened by the reduced torque.
In this case, since the same coefficient .beta. is multiplied to the duty
ratios of the pulse currents to be applied to the coils L.sub.1 and
L.sub.2, the direction of the resultant magnetic field of the coils
L.sub.1 and L.sub.2 becomes the same direction of the ones without
compensation and no indication error occurs between the two cases.
FIG. 15 shows the relationship between the rotational angle .theta. of the
pointer A and the duty ratios of the pulse currents to be applied to the
coils L.sub.1 and L.sub.2 without compensation, while FIG. 16 shows the
compensated or modified duty ratios of the pulse currents.
FIG. 14 shows still another embodiment of the cross coil type indicator
according to the present invention.
In this embodiment, a microprocessor 80 having a CPU, a RAM, and a ROM is
used instead of the F/V converter 20, the detection circuit 60, and the
current control circuit 70 in FIG. 13. In FIG. 14, the same reference
numerals shown in FIG. 13 are used to the same constructing elements.
The operation of the indicator shown in FIG. 14 will now be made with
reference to a control flow chart shown in FIG. 17.
In step S.sub.1 a, frequency of a pulse signal from the sensor 10 is
calculated and the operation moves to step S.sub.2 a, where a rotational
angle .theta. is calculated in accordance with the frequency thus
calculated.
Then, the duty ratios are calculated in accordance with sin .theta. and cos
.theta. of the rotational angle .theta. in step S.sub.3 a and the
operation goes to step S.sub.4 a, where a decision is made about whether
or not the duty ratios thus calculated are above a predetermined angle
.theta.. If the result of the decision is YES, that is, the rotational
angle .theta. is above the predetermined angle .theta..sub.1, the
operation now goes to step S.sub.5 a, where duty pulses having duty ratios
without compensation are generated by the duty pulse generating circuit 30
and they are applied to the coils L.sub.1 and L.sub.2 through the output
circuit 50.
On the other hand, when the result of the decision in step S.sub.4 a is NO,
that is, the rotational angle .theta. of the pointer A is within the
predetermined range of angle .theta..sub.1, the operation moves to step
S.sub.6 a, where the duty ratios thus calculated are multiplied by the
coefficient .beta., and in step S.sub.5 a, pulse currents having the
modified or compensated duty ratios are generated from the duty pulse
generating circuit 30 and they are applied to the coils L.sub.1 and
L.sub.2 through the output circuit 50.
It is to be noted in this case, however, that the biasing force of the
spiral spring C of the pointer A (see FIG. 1) has to be taken into
consideration when calculating the duty ratios.
As has been described about the embodiments, in the cross coil type
indicator according to the present invention, a decision is made if the
rotational angle of the pointer is within a predetermined range of angle
.theta..sub.1, and when the rotational angle of the pointer above the
predetermined angle .theta..sub.1, pulse currents having duty ratios
without compensation are generated and are applied to the coils L.sub.1
and L.sub.2. On the other hand, when the rotational angle of the pointer
is within the predetermined range of angle .theta..sub.1, pulse currents
having compensated or modified duty ratios are generated and they are
applied to the cross coils L.sub.1 and L.sub.2, thus reducing the torque
of the pointer. As a result, the generation of the noise caused by the
abutments between the pointer A and the stopper pin P can be prevented.
In the embodiments according to the present invention shown in FIGS. 8, 9,
13 and 14, the calculations of the duty ratios are shown as having been
performed in either the duty calculation circuit 30 or the microprocessor
80. It is to be apparent for those skilled in the art that digital data
corresponding to angles .theta., and at least sin .theta. may be stored in
a ROM provided in the duty calculation circuit 30 or the ROM of the
microprocessor 80 and each digital data corresponding to the rotational
angle of the pointer A and its sin .theta. can be read out of the ROM. The
data corresponding to the cos .theta. can also be obtained from the sin
.theta. data by accessing to each memory location (.theta.+90.degree.) of
the ROM without storing data about cos .theta., similar to the case shown
in FIG. 7.
However, please note that the drive circuit for driving cross coils shown
in FIG. 7 can be applied to the other cross coil type indicators besides
the indicators shown in FIGS. 8, 9, 13 and 14.
While the invention has been described in its preferred embodiments, it is
to be understood that the words which have been used are words of
description rather than limitation and that various changes and
modifications may be made within the purview of the appended claims
without departing from the true scope and spirit of the invention in its
broader aspects.
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